MARINE BIOLOGY: LECTURE 3



Biology 212, Inverts 1: Introduction, Phylum Porifera, Phylum Cnidaria

January 9, 2006

Lecture outline

I. Course overview

II. Overview of invertebrate lectures

III. What is an animal? Six characteristics (two are unique)

IV. Kingdom Animalia: Introduction to the major phyla (slides)

V. Phylogenetic overview for Kingdom Animalia. [4 min]

A. Monophyletic origin of animals from choanoflagellate [Fig. 32.3, 32.4].

B. Two views of animal diversity/evolution [Fig. 32.10, Fig. 32.11]

1. What is each based on?

2. Which one will we follow and why?

V. Phylum Porifera: the "pore bearers" or sponges

A. Sponge diversity (briefly)

B. Evolutionary relationships

1. Why considered an animal?

a) Multicellularity

b) Hox genes

2. How different from other animals (i.e. from the Eumetazoa?)

a) No true tissues

C. Structure of a simple sponge [Fig. 33.4]

1. Overview of structures

2. Focus on choanocytes: Mechanisms of water movement and feeding

3. Focus on amoebocytes: Various functions

D. Sponge sex (briefly)

E. Protection

F. Movement

V. Phylum Cnidaria ("cnid" = nettle)

A. Diversity: Hydrozoa, Scyphozoa, Cubozoa, Anthozoa

B. Evolutionary relationships

1. What key characteristic differs from Phylum Porifera?

2. What makes them different than the other Eumetazoa?

C. Body organization [Fig. 33.5]

1. Polyps and medusae

2. Key tissue layers

3. mesoglia. What is it? Where is it?

4. Gastrovascular cavity

a) Several functions…

5. Tentacles with cnidocytes (stinging cells)

6. Nervous system: nerve net

7. No other major body systems

D. Focus on the cnidocyte: structure and function [Fig. 33.5]

E. Cnidarian life-history strategies

1. Alternation of polyp and medusa forms [Fig. 33.7]

a) Basics of alternation (sexual vs. asexual reproduction)

b) Adaptive value of polyps vs. medusae

c) Which Cnidarians do this, and which don’t?

Study questions

Disclaimer: You are responsible for all material presented in class. These questions are meant to aid in your studies, but you should study the material itself, not just answers to the study questions! I suggest you learn the material and then use these study questions to quiz yourself.

1. What are the six key characteristics shared by all members of Kingdom Animalia? Be able to describe/explain each of these characteristics (i.e. know what it means to be eukaryotic, etc…). Of these, which (if any) is/are unique to Kingdom Animalia?

2. Your text mentions that both muscle and nerve tissues are unique to animals. Why are they not appropriate answers to the previous question? Think carefully about all phyla of animals.

3. Is the Kingdom Animalia currently thought to be monophyletic (in other words, that all animals originated from one common ancestor) or polyphyletic (animals originated from more than one ancestor)?

4. From the monophyletic perspective, from what type of organism is Kingdom Animalia supposed to have evolved? Name its Kingdom (pre-Animalia) as well as the more specific name of the organism, and briefly describe it.

5. What two features separate members of Phylum Porifera (and all other animals) from their protistan ancestors?

6. What does “multicellular” mean, and why don’t colonial protists qualify?

7. What are the functions of each of the following cell types or structures in a sponge? Some or all may have more than one function.

• Choanocyte (two major)

• spicule

• amoebocyte

8. Describe how water moves through a sponge, naming the major pores and passageways through which it passes as well as how the water current is generated.

9. Describe how a choanocyte is able to obtain and ingest food particles.

10. Do sponges have genders? Briefly explain…

11. How does a sponge protect itself?

12. In terms of body plan, in what two key ways do Cnidarians differ from Poriferans?

13. What are the two Cnidarian body forms? How are they similar? How do they differ?

14. What is mesoglia?

15. What is a cnidocyte? Briefly describe the structure of cnidocyte. Be sure to include specialized parts (trigger, nematocyst, operculum, etc...) Also explain what is meant by the "firing" of a nematocyst, and briefly describe how the nematocyst inflicts pain.

16. What are the three major functions of the gastrovascular cavity in cnidarians?

17. Describe the nervous system of a Cnidarian.

18. Some Cnidarians, such as Obelia (Fig. 33.7) alternate between polyp and medusa forms. (I specifically mentioned that jellyfish do this, but anemones and corals do not.) Within this type of life cycle:

• Which (polyp or medusa) reproduces asexually?

• Which reproduces sexually?

• Which is produced asexually?

• Which is produces sexually?

19. Explain the adaptive value of having a life cycle with both a polyp and a medusa phase.

Questions to begin answering and building upon as we cover Kingdom Animalia (there will be more of these types of questions in subsequent study guides).

20. Describe the key developments that are hypothesized to have occurred at each of the major branch points as the Kingdom Animalia evolved, according to the traditional model of phylogeny (i.e. body plan characteristics). In addition, explain the adaptive significance of each of the “new” or “derived” features for the animals (i.e. how does it aid in the animal’s existence?). You should also know where each of the phyla we studied should be placed on this evolutionary continuum.

21. [NOTE: This question approaches similar concepts to the previous one, but in a slightly different way.] Consider the developmental characteristics and proposed evolutionary relationships of the animal phyla we studied. For each phylum studied, you should know:

• symmetry

• number/type of tissue layers (or whether it has them at all)

• body cavity: whether it exists, and type

• considered Protostome, Deuterostomes or neither

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